Construction World June 2022

Keller’s diverse product offering allowed the design team to come up with efficient and innovative solutions. The optimised design made use of four different pile types and seven different pile sizes. Driven Cast-in-Situ piles The majority of the piles were of the Driven-Cast-In-Situ type (known as Franki piles) and is a staple product offered by Keller. This pile type is typically very cost effective, has good load bearing capacity and is well suited to the tricky ground conditions encountered in Cape Town. These versatile piles were installed in two variants, compression only piles and tension/compression piles. The tension capacity was improved by retrofitting a rock anchor which is installed into the bedrock below the toe of the pile. This anchor forms an integral part of the pile. The anchor enables the pile to also transfer tension loads to the bedrock during certain seismic occurrences. Also worth mentioning is that Keller’s use of dedicated piling rigs take up far less space compared to crane mounted pile driving leaders and offers a real benefit in projects with space constraints and interfaces with other work. This piling method offers good production and assures the achievement of contracted milestone dates. ODEX piles On the northern site boundary, a new culvert was constructed requiring a relatively deep excavation adjacent to existing services and trees. The presence of the trees precluded the use of a typical batter slope, anchors or a crane requiring high headroom. To satisfy all three constraints, Keller provided an alternative design to the initially planned sheet pile solution. The alternative design made use of reinforced ODEX type piles installed in a row and socketed into the bedrock. This system provides a cantilever to support the embankment.

Left: Demolition of existing structures to make way for the new building. Right: Dowelling for tension capacity in piles.

New stormwater culvert with cantilever lateral support in the background supporting the protected tree.

warranted the application of temporary cased auger piles. Again, Keller designed a number of these piles to work in compression as well as tension. Tension capacity was achieved in two manners: retrofitted rock anchors and in some instances, piles were socketed into bedrock. Where rock sockets were chosen, the resistance to friction gained from the interface between the pile’s concrete and the rock socket enables tension loads to be transferred into the bedrock. Micro piles The last type of pile that were installed were micro piles. These piles use smaller rigs and are particularly useful to install piles to support new structural elements in and around existing buildings. This is achieved by using a miniature drill rig that can fit through narrow door openings and requires

ABOUT KELLER GEOTECHNICS SA Keller, is the largest, oldest and most established specialist geotechnical contractor in Sub-Saharan Africa, offering a comprehensive range of For any enquiries, please contact Anton Stoll on 082 419 0249 or anton.stoll@keller.com More information: www.keller-africa.co.za This prestigious project highlights the versatility and capability of the Keller team – from design to installation – to deliver a complex turnkey design and construct geotechnical project.  geotechnical and marine engineering techniques. very little headroom, making it suitable to manoeuvre and install piles inside buildings and below existing floors and ceilings.

This innovative cantilevered design assured slope stability without the need of anchors, avoiding potential clashes with

existing public services. In addition, the equipment required for the ODEX piles took up limited headroom which safeguarded the trees. Temporary cased auger piles In certain areas of the building footprint, the structural loads

19 CONSTRUCTION WORLD JUNE 2022